Employee Benefit Plans - Changes in Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss) arising during the year	$ 5,305	$ (426)	$ (10,360)
Amortization of actuarial (gain) loss	1,238	1,353	900
Total	6,543	927	(9,460)
OPEB
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss) arising during the year	240	282	949
Amortization of actuarial (gain) loss	(146)	(99)
Prior service credit	(688)	(698)	(800)
Total	$ (594)	$ (515)	$ 149